An important process for the production of acetic acid is the carbonylation of an alkyl alcohol, especially methanol, and reactive derivatives thereof, with carbon monoxide in a liquid reaction medium. Such carbonylation reactions are generally carried out in the presence of a catalyst, e.g., a Group VIII metal catalyst such as rhodium and iridium, a halogen containing catalyst promoter, e.g., methyl iodide, and water. U.S. Pat. No. 3,769,329 discloses the use of a rhodium-based carbonylation catalyst dissolved, or otherwise dispersed, in a liquid reaction medium or supported on an inert solid, along with a halogen-containing catalyst promoter as exemplified by methyl iodide. However, it is understood that various catalyst systems, particularly those incorporating Group VIII metals, may be used for the production of acetic acid through the carbonylation of methanol. Generally, the carbonylation reaction is conducted with the catalyst being dissolved in a liquid reaction medium through which carbon monoxide gas is continuously bubbled. U.S. Pat. No. 3,769,329 discloses that water may be added to the reaction mixture to exert a beneficial effect upon the reaction rate, and water concentrations between about 14 wt. % to about 15 wt. % are typically used. This is sometimes referred to as the “high water” carbonylation process.
An alternative to the “high water” carbonylation process is the “low water” carbonylation process, as described in U.S. Pat. No. 5,001,259, U.S. Pat. No. 5,026,908, and U.S. Pat. No. 5,144,068. Water concentrations below 14 wt. % can be used in the “low water” carbonylation process. Employing a low water concentration simplifies downstream processing of the desired carboxylic acid to its glacial form. The more water there is in a reaction stream, the greater the operating costs to remove water from the product acetic acid and the greater the capital investment in product recovery and purification equipment. The efficiencies achieved when operating at very low water concentrations makes it attractive to operate at the lowest water concentration possible. However, when reducing the reactor water to minimize operating and fixed costs, it is more difficult to maintain acceptably high rates of acetic acid production with good catalyst stability since the rate of the reaction decreases as the reactor water is decreased as explained in U.S. Pat. No. 5,026,908.
Other methods of producing acetic acid include the catalytic oxidation of ethylene. Numerous methods are known for the catalytic oxidation of ethylene to acetic acid. See, for example, U.S. Pat. Nos. 6,605,739; 3,792,087 and 3,970,697.
Vinyl acetate is a well-known industrial chemical. The production of vinyl acetate from ethylene, oxygen and acetic acid using conventional vinyl acetate catalysts is known in the art. Vinyl acetate is typically used as a raw material for vinyl resins such as polyvinyl acetate. Historically, vinyl acetate was primarily manufactured from the vapor phase reaction of ethylene, acetic acid and oxygen with a zinc acetate catalyst. More recently, vinyl acetate is often produced from the vapor-phase reaction of ethylene, acetic acid and oxygen, with palladium-based catalyst systems. For example, it is known to produce vinyl acetate by reaction of ethylene, oxygen and acetic acid using a catalyst comprising palladium and gold, supported on a carrier as described in U.S. Pat. No. 6,303,537. For other exemplary processes, see U.S. Pat. Nos. 3,190,912; 3,637,819; 3,650,896; 4,370,492; 4,902,823, and 5,185,308.
Conventionally, acetic acid and vinyl acetate are produced independently of each other. In other words, vinyl acetate is frequently produced from ethylene wherein a first process involves reacting the ethylene to form acetic acid, followed by a second process of reacting a mixture of the acetic acid and ethylene to produce vinyl acetate.
However, some processes are known to integrate production of the two products in various degrees. For example. U.S. Pat. No. 6,180,821 describes the production of acetic acid and/or vinyl acetate from ethylene, or ethane, using a first reaction zone with a catalyst active for the oxidation of ethylene to acetic acid and/or active for the oxidation of ethane to acetic acid, ethylene and carbon monoxide, and a second reaction zone containing a catalyst active for the production of vinyl acetate. The Patent indicates that an advantage of the integrated process is the heat of the first reaction zone product reduces the need to heat the feed to the second reaction zone. U.S. Pat. No. 4,188,490 relates to a catalytic oxidation process for the production of mixtures of acetic acid and vinyl acetate comprising the step of contacting a feed mixture containing ethylene, oxygen and water, as steam, with a catalyst composition to provide a mixture of acetic acid and vinyl acetate. The catalyst system comprises a palladium metal on a zinc oxide support treated in the presence of a sulfur modifier. The method requires the subsequent step of fractional distillation to separate the acetic acid from the vinyl acetate.
U.S. Pat. Nos. 6,420,595 and 6,605,739 disclose additional integrated processes for the production of acetic acid and vinyl acetate.